Electromagnetic transmission



Patented June 19, 1934 UNITED STATES PATENT omes This invention relatesto electro-magnetic transmissions and particularly to that type of powertransmissions operable by rotary, electromagnetic members.

The principal object of the present invention is the provision of anelectro-magnetic power transmission whereby the speed of the driving anddriven members are synchronized without the use of any mechanicalconnections therebetween.

Another object of this invention is the provision of an electro-magneticpower transmission having means whereby the driven member may be movedat a gradually increasing rate of speed as the driving member maintainsa substantially constant rate of speed and whereby the driving anddriven members will be locked together when a predetermined relativespeed is attained.

Further objects of the invention are to provide a simple'and efficienttransmission which affords great flexibility and durability andeliminates vibrating to a large extent. Referring to the drawing:

Figure 1 is a sectional view of an electric power transmission with theelectrical circuit diagrammatically shown and embodying this invention.

. Fig. 2 is a sectional view partly broken away, taken on line II-II ofFig. 1 with the electrical circuit shown diagrammatically.

Fig. 3 is a diagrammatical view of the frequency responsive switch withsome of the connecting parts.

.In the drawing like reference characters refer to similar parts and thenumeral 10 indicates a power driving shaft which is driven by anysuitable prime mover, such as steam engine, internal combustion engine,electric motor, etc., not shown. Securely mounted on driving shaft 10 isa housing 12, preferably made of iron and having a tubular portion 14which is adapted to be rotated concentrically with drive shaft 10.

Within the tubular portion 14 of housing 12 is a series ofelectro-magnetic poles 16 which are securely attached in radial positionby screw 18 or by any other suitable means. About each of the poles 16is wounda coil. 20 of suitable electric conducting nature. These coilsare connected in series in such a manner that when a direct current ispassed through the circuit, adjacent inner portions of poles 16 will beof opposite polarity. As shown in Fig. 1, an exciter dynamo 22, drivenby the driving shaft 10 through the intermediacy of pulleys 24 and 26and belt 28, is in electrical connection with coils 20 through wires 30and 32 which connect with brushes 34 and 36 respectively. These brushesin turn contact slip collector rings 38 and 40 respectively. Rings 38and 40 rotate with the housing and are connected respectively with wires42 and 44 so that when the shaft 10 is rotated a circuit will passthrough all of the coils 20 thereby producing a series ofelectro-magnets alternately of north and south poles and revolving atthe same rate of speed as the driving shaft 10. The rheostat 45 isplaced in the circuit to vary the resistance to properly control thecurrent to the coils.

Positioned in axial alinement with shaft 10 is a driven shaft 46 whichmay be adapted to drive any suitable load. This driven shaft may bejournaled in housing 12 as shown in Fig. 1 to maintain the shafts inproper alinement; however, this may be accomplished in many othersuitable ways than that one now in common usage. Keyed to shaft 46 at 47is an armature 48 made up of a solid center portion 50 to which issecured a series of laminated pole pieces 52 which correspond in numberto. the poles 16. I

Each pole piece 52 is provided with a coil 54 of conducting material andthese coils are connected in series in such a manner as to cause ad- 3jacent poles to have opposite polarity when a proper electric current ispassed through the circuit. This series of coils 54 is furnished directcurrent from the exciter dynamo 22 through wires 56 and 58 which arejoined to wires 30 and 5' 32 respectively and to the brushes 60 and 62which contact slip rings 64 and 66 respectively. These slip rings aresecurely attached to drive shaft 46 and in series with coils 54. Each ofthe pole pieces 52 is provided at its outer edge with a series of copperbars 68 positioned parallel with shaft 46 with their ends connected withshort circuiting rings 70, thus forming the well known squirrelcagecommonly used as a secondary winding for an induction motor. The housing12 with its attached parts and the armature 48 comprise two memberspositioned one within the other and fixed respectively on two rotatableshafts that are in alinement. These two members are spaced apart aslight distance to form an air gap therebetween.

It is desired to close the circuit to coils 54 only when the two membershave attained predetermined relative speed, and for this purpose thespecially constructed automatic switch or relay 72 is placed in thearmature coil circuit. This switch '72 is so constructed that it may beadjusted to close the circuit at any predetermined frequency of thecurrent set up in the armature. While this type of switch is described,yet'it is apparent that other means including purely mechanicalconstruction might be used effectively to obtain the desired resultsSwitch 72 is shown more in detail in Figure 3, and consists of an arm'74 pivotally mounted at 76 and provided with an armature78 formedintegral therewith. Armature '78, during the starting period, is helddown by the magnetic pull of coil 80 which is in circuit with coils 54through the bushes 60 and 62. In the circuit with coil 80 is a switch 82which is held in the closed position during the time that arm '74 is inthe open or raised position, and which is in the open position when saidarm moves downwardly to the closed position, which arm 74 would normallymove from the open to the closed position by gravity, yet it is deemedbest to provide a spring 86 which retracts to draw the arm to the closedposition when the frequency of the current passing through coil 80 isdecreased to a predetermined amount.

In the circuit as above described it is very evident that as thefrequency decreases the current passing through the coil 80 alsodecreases, thus permitting the release and closing of switch '72. Thistype of switch has been shown because of its simplicity; however, it isvery apparent that a primarily frequency responsive switch might besubstituted for 72 without altering the general functioning of thedevice.

In the operation of this power transmission it is assumed that shaft 10with its connected parts, including the electro-magnets, is being drivenat a substantially uniform rate of speed by a prime mover that issuitable to drive the load that is to be driven through the means of thetransmission and driven shaft 46. With the rheostat in the off positionas shown in Fig. 1, the armature 48 and shaft 46 will remain stationary.Switch '72 is in the open position and will not close until a certainrelative speed of the two members is attained as hereinafter set forth.

Since the starting torque of the driven load is relatively high, theload is accelerated by means of rheostat 45 which varies the resistancein the circuit of the direct current from the exciter 22 to the coils20. As rotating energized field cuts the lines of force of the armaturea heavy current is induced in the squirrel cage, so that the armaturewill rotate in the same direction as the fields, and at an accelerationgoverned by the rheostat. After the starting toroue has been overcomethe armature will lag behind the rotating field enough to cause thecutting of a suflicient number of lines of force to maintain the drivenload at a constant speed. This slip varies, but usually is about fourpercent at full load.

When this minimum slip has been reached it is desired to sufficientlyenergize the field coils and the armature coils so that a sufficientmagnetic flux will be produced to cause the fields and armature torotate at the same rate. This is accomplished by the closing of theautomatic switch or relay '72 when the predetermined frequency of theinduced alternating current in coils 54 is reached. It is well knownthat the frequency of the induced current varies as the relative speedsof the field and armature vary. When switch 72 is closed a directcurrent from the exciter energizes coils 54 as well as the field coils20. This causes the armature to lock itself with the rotating field withthe north poles of the field attracting the south poles of the armatureand vice versa. Thus the two members will rotate in absolute synchronismand will so continue as long as the prime moving force is sufficient todrive the load at its attained speed.

By proper connections the switch or relay is closed by means of thepredetermined low frequency current produced in the coils 54 when theminimum slippage between the two series of electro-magnets is reachedand when said switch is closed the combined force of the squirrel cageand the direct-current energized coils 54 will be sufficient to step thetwo rotating members into synchronous movement after which they will beheld in locked position under normal running conditions.

When these two rotating members become synchronized there will be norelative movement of the members, therefore no lines of force will becut and no alternating current induced in the squirrel cage or armaturecoils, thereby eliminating the usual alternating current losses such ashysteresis, and eddy currents in the laminations, copper losses in thesquirrel cage windings, etc. Should the load become too great for theelectromagnet force to carry the armature will fall out of step with therotating field and again induce alternating current in the squirrel cageand drive the load at a slower rate of speed until such time when theload lightens when the speed of the two members will again lock in step.With this electro-magnetic connection of parts no sudden shocks orvibrations will be imparted to either the driving or driven members.

The present electro-magnetic power trans-' mission above described isadapted to start a load, accelerate its movement and lock the drivingand driven members together so that they are synchronized while inspaced apart relation.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. An electro-magnetic power transmission comprising two memberspositioned in operative relation and fixed respectively to a drivingshaft and a driven shaft in axial alinement; a series of electro-magnetscarried by one of said members; a series of electro-magnets and asquirrel cage winding carried by the other of said members; electricalmeans whereby said first named series of electro-magnets is energized todrive said second named member and whereby said second named series ofelectro-magnets is energized when a predetermined relative speed of thetwo members is attained.

2. An electro-magnetic power transmission comprising two members, inoperative relation, respectively, fixed to a driving shaft and a drivenshaft in alinement; a series of electro-magnets carried by the membermounted on said driving shaft; a series of electro-magnets carried bythe member fixed to said driven shaft; cylindrical arranged copper barswith their ends connected with short circuiting rings carried by themember fixed to said driven shaft; and electrical means whereby saidfirst named series of electro-magnets is energized to drive said secondnamed series of electro-magnets at an accelerating speed and then tosynchronize the speed of both series of electromagnets.

3. An electro-magnetic transmission comprising a series ofelectro-magnets carried by a driving shaft; a. series of electro-magnetsand a squirrel-cage winding mounted on a driven shaft and in operativerelation with said first named series of electro-magnets; and electricalmeans adapted to first energize the magnets on said driving shaft torotate said driven shaft and then named series of electro-mag'nets isenergized, while being rotated, to drive said driven shaft up togapredetermined speed when the other of said series of electro-magnets isenergized to lock together the two series of electro-magnets tosynchronize the movement of the driving anddriven.

shafts.

FANNON F. BEAUCHAMP.

